1. Field of the Invention
The present invention relates to a non-break change-over device used for a redundancy system adapted to be multiplexed by using an active system and a standby system, which enables each of these two systems to be switched alternately, thus achieving an improvement of reliability.
2. Description of the Related Art
A redundancy system has been conventionally adopted in such transmission equipment and the like as require high reliability, which is designed to multiplex each of functional blocks, circuit boards or transmission paths constituting the transmission equipment by utilizing an active system and a standby system. In such a system, for example, a monitoring section loaded with firmware has been used to monitor each of multiplexed components of the device.
When a necessity occurs for, for instance, maintenance and checking in one information transmission system functioning as an active system, a switching signal providing instructions for switching from the standby state to an active state is fed from the monitoring section to the other information transmission system functioning as a standby system. When the standby system receives, from the firmware, an instruction for switching, an external switching signal is sent to the active system and thus switching between standby and active systems can be achieved through this mutual signal communications with a matched timing.
If a standby system receives, from the firmware, an instruction for switching, it sends out a switching request signal to an active system and, at the same time, it internally generates a switching signal and performs switching control therein. Because both frame pulses each controlling the active and standby system respectively have the same period, if these frame pulses are in phase with each other, switching between the active and standby systems can be achieved at a stroke within the same frame. However, due to a time-delay caused by a difference in the transmission paths extending from the same generating source, and to other conditions, these frame pulses for each system are not always in phase with each other. Accordingly, in the case where the frame of the active system leads slightly that of the standby system, if input timing of a switching instruction from the firmware is not matched, a switching of the standby system to an active state within the frame during which switching of the active system to a standby state has been performed cannot be achieved, causing any system not to function as an active one, i.e., possibly no operations of any system in some cases.
FIG. 8 shows a conventional redundancy system having first and second information transmission systems and a conventional non-break change-over device provided in relation thereto. The first and second information transmission systems, 1 and 1xe2x80x2 are, for example, information processing devices which deal with information in units of frames defined by frame pulses having the same period and both of them have the equivalent functions. The conventional non-break change-over device 2 is provided which constitutes the redundancy system together with both information transmission systems 1 and 1xe2x80x2.
The non-break change-over device 2 is provided with a monitoring section comprising firmware into which a monitoring program is stored. Also, the non-break change-over device 2 is provided with control sections 4 and 4xe2x80x2, first D flip-flops 5 and 5xe2x80x2 and second D flip-flops 6 and 6xe2x80x2 corresponding to the information transmission systems 1 and 1xe2x80x2 respectively.
Both of these information transmission systems 1 and 1xe2x80x2 are equipped with control circuits 1a and 1axe2x80x2 which are in advance set so that one information transmission system functions as a standby system and the other as an active system.
The monitoring section 3 is used to monitor the operational states of both the information transmission systems 1 and 1xe2x80x2 and to send out a switching instruction signal 7 to either of control sections 4 or 4xe2x80x2 corresponding to either of the information transmission systems 1 or 1xe2x80x2 which is then functioning as a standby system when switching between the active and standby systems is required, including a case where malfunctions have occurred which are so slight as not to cause a stop page of transmission operations of currently operating information transmission systems 1 or 1xe2x80x2, or a case where a necessity for maintenance and checking occurs in currently operating information transmission systems 1 or 1xe2x80x2.
For example, while one information transmission system 1 is functioning as a standby system, if the control section 4 corresponding to this information transmission system 1 receives a switching instruction signal 7, it feeds a switching request signal 8 to the control section 4xe2x80x2 corresponding to the other information transmission system 1xe2x80x2 and at the same time transfers a switching instruction signal 7 to the first flip-flop 5 corresponding to said information transmission 1.
The first flip-flop 5 to which the switching instruction signal 7 is transferred from the control section 4, when it receives a frame pulse 9 from the corresponding information transmission system 1, feeds an output signal 10, based on the transferred switching instruction signal 7, to the second flip-flop 6. When the second flip-flop 6 receives a switching timing pulse 12 from a switching timing pulse generating section 11, it outputs an internal switching signal 13, based on the output signal 10 sent from the first flip-flop 5.
The internal switching signal 13 from the second flip-flop 6 is outputted as a switching signal for switching to an active state to the control circuit 1a of the information transmission system 1 functioning as a standby system, by which switching of the information system 1 from its standby state to an active state is achieved accordingly.
On the other hand, the currently operating control section 4xe2x80x2, when it receives a switching request signal 8 from the control section 4 of said one information transmission system 1, outputs a switching request signal 8xe2x80x2 and a switching instruction signal 7xe2x80x2. The standby control section 4 receiving the switching request signal 8xe2x80x2 from the control section 4xe2x80x2, because it has received said switching instruction signal 7 from the monitoring section, does not respond to the switching request signal 8xe2x80x2 and ignores it. Also, when the first flip-flop 5xe2x80x2 receiving the switching instruction signal 7xe2x80x2 from the control section 4xe2x80x2 is given a frame pulse 9xe2x80x2 from the corresponding information transmission system 1xe2x80x2, it outputs an output signal 10xe2x80x2 to the second flip-flop 6xe2x80x2 based on the switching instruction signal 7xe2x80x2 as in the case of the first flip-flop 5 of the standby system.
The second flip-flop 6xe2x80x2, when it receives a switching timing pulse 12xe2x80x2 from a switching timing pulse generating section 11xe2x80x2, outputs an internal switching signal 13xe2x80x2 based on the output signal 10xe2x80x2 from the first flip-flop 5xe2x80x2.
The internal switching signal 13xe2x80x2 from the second flip-flop 6xe2x80x2 is fed as a switching signal for switching to a standby state to said control circuit 1axe2x80x2 of the information transmission system 1xe2x80x2 functioning as an active system, by which switching of the information transmission system 1xe2x80x2 from its active state to a standby state is achieved accordingly.
Each of the switching timing pulse generating section 11 and 11xe2x80x2 provided corresponding to each of the information transmission system 1 and 1xe2x80x2 produces switching timing pulses 12 and 12xe2x80x2 respectively, based on the frame pulses from each of the information transmission systems 1 and 1xe2x80x2. Each of the timing pulses 12 and 12xe2x80x2 has the same period as the frame pulses 9 and 9xe2x80x2 respectively and also is by about half the period out of phase with the frame pulses. As described above, there is a case where the frame pulse, which is generated based on a clock signal from one clock generating source, from the currently operating information transmission system 1 or 1xe2x80x2 slightly leads that of the standby information transmission system 1 or 1xe2x80x2 due to a time-delay caused by difference in transmission paths to each of the information transmission systems 1 and 1xe2x80x2.
FIG. 9 is an operational timing chart of the conventional non-break change-over device 2 observed when the frame pulse from an active system slightly leads that from a standby system.
In FIG. 9, the timing of signals is illustrated including the internal switching signal 13, switching request signal 8 and the like based on the frame pulses 9 and 9xe2x80x2 and switching timing pulses 12 and 12xe2x80x2 from both active and standby systems.
The internal reference frame pulses 9 shown in FIG. 9 (a) are frame pulses used to control the timing in the standby information transmission system comprising a group of pulses having their pulse peaks (P1, P2 and P3) at time t1, t2 and t3 respectively. The switching timing pulses 12 shown in FIG. 9 (b) are a group of pulses (P4 and P5) each having the same period as the frame pulse 9 and each being by half the period out of phase with the frame pulse 9. The frame pulse 9 for the active system has the same period as the frame pulse 9xe2x80x2 for the standby system and the frame pulse 9xe2x80x2 from the active system slightly leads that of the frame pulse 9 from the standby system. Also, the switching timing pulse 12xe2x80x2 from the active system has the same relation with respect to its frame pulse 9xe2x80x2 as in the case for the standby system.
As shown in FIG. 9 (c), the Low (L) level of the switching instruction signal 7 from the monitoring section 3 represents a switching instruction to be given to the standby system and the High (H) level to the active system. That is, after the switching instruction signal 7 as shown in FIG. 9 (c) is inputted from the monitoring section 3 immediately after the time t1 to a control section, i.e., an external switching circuit 4 of the standby system shown in FIG. 8, this switching signal 7 is then outputted, by the pulse 2 at the subsequent time t2, as an output signal 10 from the first flip-flop 5 to the second flip-flop, i.e., an internal switching circuit 6. As shown in FIG. 9 (d), the output signal 10 being fed to the internal switching circuit 6, after the internal switching circuit has received a pulse P5, i.e., the switching timing pulse 12 given after the time t2, is outputted as an internal switching signal 13, as shown in FIG. 9 (e) from the internal switching circuit 6 to the control circuit 1a of the information transmission system 1 in the subsequent frame following the frame between the time t1 and t2. By this switching function of the control circuit 1a receiving the internal switching signal 13, switching of the information transmission system 1 from its standby state to an active state is achieved accordingly.
Also, when the switching instruction signal 7 is fed immediately after the time t1 to the external switching circuit 4, as shown in FIG. 9 (f), the signal 7 with the level of the signal inverted is outputted as a switching request signal 8 to the currently operating control section, i.e., the external switching circuit 4xe2x80x2 of the active system.
When the control section 4xe2x80x2 of the active system receives a switching request signal 8 from the control section 4 of the standby system as shown in FIG. 9 (i), the signal 8 is transferred as a switching instruction signal 7xe2x80x2 to the first flip-flop 5xe2x80x2. If the first flip-flop 5xe2x80x2 receives the frame pulse 9xe2x80x2 the phase of which slightly leads that of the frame pulse 9, as shown in FIG. 9 (), it switches its output from an H level to an L level at the time when the pulse P6 is given. The second flip-flop 6xe2x80x2 receiving the above output 10xe2x80x2, when it receives a pulse P9, i.e., the switching timing pulse 12xe2x80x2, causes the output signal 10xe2x80x2 to be fed as an internal switching signal 13xe2x80x2 from the internal switching circuit 6xe2x80x2 to the control circuit 1axe2x80x2 of the information transmission system 1xe2x80x2. By the switching function of the control circuit 1axe2x80x2 receiving this internal switching signal 13xe2x80x2, switching of the information transmission system 1xe2x80x2 from its active state to a standby state is achieved accordingly.
FIG. 10 is an explanatory drawing of above-described switching states in relation to pulse frames from the active and standby systems. The states are described hereinafter by referring to FIG. 10 wherein the control section 4 corresponding to the standby system receives the switching instruction signal 7 at the time between the head positions of corresponding frame F1 and F1xe2x80x2 when the frames F1, F2 and so on from the active system slightly lead the frames F1xe2x80x2, F2xe2x80x2 and so on from the standby system. Under this condition, in the standby system, when the first flip-flop 5 receives a frame pulse 9 (P2), an output signal 10 is fed at the time t2 from said first flip-flop 5 to the second flip-flop 6 and when this second flip-flop receives a switching timing pulse 12 (P5), an internal switching signal 13 is outputted from the second flip-flop 6. Therefore, in the standby system, switching from its standby state to an active state occurs during frame F2 following frame F1 where the switching instruction signal 7 is received.
On the other hand, in the active system receiving a switching request signal 8 from the standby system, when the first flip-flop 5xe2x80x2 receives the frame pulse 9xe2x80x2 (P6), an output signal 10xe2x80x2 is fed from the first flip-flop 5xe2x80x2 to the second flip-flop 6xe2x80x2 and when the second flip-flop 6xe2x80x2 receives a switching timing pulse 12 (P7), an internal switching signal 13xe2x80x2 is outputted from the second flip-flop 6xe2x80x2. Therefore, in the active system, switching to a standby state occurs during the frame F1xe2x80x2 corresponding to the frame F1.
For this reason, although the switching from the active system to the standby system is carried out during the frame F1xe2x80x2, the switching from the standby system to the active system is carried out not during the frame F1 corresponding the frame F1xe2x80x2 but during the subsequent frame 2, causing lack of information during substantial one frame. Thus, in the conventional non-break change-over device, there has been a problem of the lack of information corresponding to one frame in the switching operation.
The object of the present invention is, therefore, to provide a non-break changeover device which does not cause lack of information in the switching operations between an active system and a standby system regardless of the state of input timing of a switching instruction signal to be fed from a monitoring section even under the condition where a frame from the active system slightly leads that from the standby system.
Another object of the present invention is to provide a non-break change-over system which does not cause the lack of information in the switching between an active system and a standby system.
According to the present invention, a non-break change-over device is provided for complementarily switching first and second information transmission systems between an active state and a standby state and for constituting a redundancy system together with the both information transmission systems each having the same functions and each handling information in units of frames defined by frame pulses having the same period each other, comprising a monitoring section used to monitor each of the information transmission systems and to generate a switching instruction signal used to switch one information transmission system functioning as a standby system to an active system when a necessity occurs for switching the said information transmission system between the active state and standby state, an internal switching circuit provided corresponding to each of the information transmission systems which is used, when the internal circuit corresponding to one information transmission system described above receives a said switching signal from the monitoring section, to generate an internal switching signal which is outputted in synchronization with timing pulses each having the same period as the frame pulse from the other information transmission system but being out of phase with said frame pulse in order to cause the other information system to b transmission system e switched to an active state, an external switching circuit provided corresponding to each of the information transmission systems which is used, when the external switching circuit corresponding to said one information transmission system described above receives the switching signal from the monitoring section, to output a switching request signal to the internal switching circuit of the said other information transmission system in order to cause the other information transmission system that was functioning as an active system to operate as a standby system, and a delay circuit provided corresponding to each of the information transmission systems which is used to give a time-delay to a switching request signal to be fed from the external switching circuit of one information transmission system to the internal switching circuit of the other information transmission system in order to perform switching operations between the standby state and active states in said information transmission systems within the same frame of pulses from both information transmission systems.
Each timing pulse for each of the information transmission systems is by about half the period out of phase with the frame pulse from each of the corresponding information transmission systems.
Said internal switching circuit corresponding to one information transmission system that was functioning as a standby system receives the switching instruction signal from the monitoring section through the external switching circuit of the other information system and also this internal switching circuit corresponding to one information transmission system outputs the internal switching signal during the subsequent frame following the frame during which the external switching circuit of the other information transmission system has received the switching instruction signal and also, at the time of the head of the frame following the frame described above, the external switching circuit corresponding to one information transmission system outputs the switching request signal toward the internal switching circuit of the other information system that was functioning as an active system.
The delay circuit operates in synchronization with the frame pulse from either of the information transmission systems corresponding to the delay circuit, comprising a first holding circuit to hold the switching request signal to be sent to the other information transmission system when the frame pulse is received, and also each of the internal switching circuits operates in synchronization with the timing pulse from either of the corresponding information transmission systems, comprising a second holding circuit to hold the switching request signal fed by the first holding circuit when the timing pulse is received.
The first and second holding circuits can be constructed by using flip-flops.
The flip-flops can be constructed by using D flip-flops.
Another aspect of the present invention is that provides a non-break change-over device for complementarily switching first and second information transmission systems between an active state and a standby state and for constituting a redundancy system together with the both information transmission systems each having the same functions and each handling information in units of frames defined by frame pulses having the same period each other, comprising a monitoring section used to monitor each of the information transmission systems and to generate a switching instruction signal used to switch one information transmission system functioning as a standby system to an active system when a necessity occurs for switching the information transmission system between the active state and standby state, a first flip-flop provided corresponding to each of the information transmission systems, wherein said first flip-flop corresponding to one information transmission system, when it receives the switching instruction signal from the monitoring section, is used to output a switching request signal, in synchronization with the frame pulse of one information transmission system, to cause the other information transmission system to function as a standby system or one information transmission system to function as an active system, or said first flip-flop provided corresponding to the other information transmission system, when it receives the switching request signal from the first flip-flop provided corresponding to one information transmission system, is used to output a switching request signal, in synchronization with the frame pulse of the other information transmission system, to cause the other information system to function as a standby system, and a second flip-flop provided corresponding to each of the information transmission systems, wherein the second flip-flop, when it receives the switching request signal fed by the first flip-flop corresponding to the information transmission system for which this second flip-flop is provided, is used to output an internal switching signal to the information transmission system in synchronization with a timing pulse having the same period as the frame pulse from the information transmission system for which the second flip-flop and being out of phase with the above frame pulse, characterized in that switching operations of one information transmission system to an active state performed by the switching request signal from the second flip-flop corresponding to one information transmission system and of the other information transmission system to a standby state by the switching request signal from the second flip-flop corresponding to the other information transmission system occur during the same frame corresponding to both information transmission systems.
During the subsequent frame following the frame during which the first flip-flop corresponding to one information transmission system that was functioning as the standby system has received the signal corresponding to the switching instruction signal from the monitoring section, the second flip-flop corresponding to one information transmission system outputs the internal switching signal, and also the second flip-flop corresponding to one information transmission system that was functioning as the standby system outputs, at the time of the head of the frame following the frame described above, the switching request signal to the first flip-flop corresponding to the other information transmission system that was functioning as the active system.
Between the monitoring section and each of the first flip-flops, a control section may be provided which is used to output the switching instruction signal or the signal corresponding to the switching request signal to the corresponding first flip-flop when the switching instruction signal is received from the monitoring section or the switching request signal from the first flip-flop of one information transmission system receiving the switching instruction signal.
The control section provided corresponding to one information transmission system, when it receives the switching instruction signal from the monitoring section and even if it receives the switching request signal from the first flip-flop provided corresponding to the other information transmission system, neither respond to this switching request signal nor output said signal to the first flip-flop provided corresponding to said one information transmission system.
Between the monitoring section and each of the first flip-flops, a control section is provided which is used to output the signal corresponding to the switching instruction signal to the corresponding first flip-flop when the control section receives the switching instruction signal from the monitoring section and the switching request signal fed by the first flip-flop provided corresponding to one information transmission system is inputted to the second flip-flop provided corresponding to the other information transmission system, and the second flip-flop, when it receives the switching request signal from the first flip-flop, outputs the internal switching signal in order to cause the other information transmission system to function as the standby system in synchronization with the timing pulse for the other information transmission system.